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Thread: measuring Thiele-Small parameters - what am I missing?

  1. #51
    Join Date: Nov 2011

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    I'm frank.

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    FWIW, Just out of curiosity I ran some quick tests with my DATS2; Fs of 385HPD and 3833 didn't change vertical or on their backs.
    I've also seen vids both Tannoy and ATC measuring QC T&S with driver clamped face down into a test enclosure. I think if a cone sags when driver is on its back the spiders are buggered.

  2. #52
    Join Date: Jun 2008

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    I'm Steve.

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    Quote Originally Posted by cooky View Post
    FWIW, Just out of curiosity I ran some quick tests with my DATS2; Fs of 385HPD and 3833 didn't change vertical or on their backs.
    I've also seen vids both Tannoy and ATC measuring QC T&S with driver clamped face down into a test enclosure. I think if a cone sags when driver is on its back the spiders are buggered.
    Thanks Frank. I have the driver out of the enclosure now. I will measure the simple stuff and then bolt the driver facing into the enclosure to do the Vas measurement. Having had a quick look it seems I need to calculate the volume enclosed by the cone and add it to the box volume. I am now in the process of knocking up 4 covers for the ports that will block only the outside end and leave the end inside the enclosure open so as not to detract the 4 port volumes from the results. I think that is the best way unless I get some more informed advice.

    Steve

    Sent from my SM-G960F using Tapatalk
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  3. #53
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Like I said, the difference between vertical and horizontal measurements depends on the driver. It's a lot more with some drivers than others. It isn't difficult to verify. They don't have to be buggered for it to make a difference.

  4. #54
    Join Date: Jan 2013

    Location: Durham - UK

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    I'm Ken.

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    Quote Originally Posted by RothwellAudio View Post
    Yes, there's nothing wrong with making the test equipment as accurate as it can be. My point really was that the whole Thiele/Small approach to vented box design isn't as accurate as the computer read-outs might lead you to believe. Certainly, you can enter lots of data and the computer will crunch the numbers and give you the -3dB point to 100th of a Hz, but it's really only a guide.

    Yes, you measure the driver in free air and again with some added mass or mounted in a test enclosure. However, the free air resonance changes if you have the driver laying face up. The change seems to be a lot more for some drivers than others, but certainly more than 1%. Personally, I wouldn't want to go to the expense of calibrating the system with a 0.01% resistor and then introduce bigger errors by doing the measurements with the driver face up.

    Neither am I.
    DATS has a lot of functions other than T&S perimeters, Signal Generator, Oscilloscope, so calibration is worth while.

    Agreed T&S Parameters and box calculators give ball park results which need fine tuning.

    You still missed my point on the measuring, Its the difference between the two measurements on its back, or the difference between the two mounted vertical. I realize they will be different sets of measurements.
    The driver will have a pair of measurements on its back and a pair mounted vertical.
    But will the DIFFERENCE between the bare/Loaded measurements be the same for both attitudes?
    I don't know how you would load a vertical driver anyway, you would have to use one of the other methods.

    This software is used by many people and also Dayton Audio, who designed the software for in house use, before selling it to the public. I've seen the DATS logo in the corner of other manufacturer info as well, so it must work.
    Maybe the software takes account of the driver orientation, who knows.
    Seems pretty pointless trying to think of reasons it might not work, when you don't know what the designers have taken into account in the software.
    Measure a driver with known properties and the measurements are damn close to them, close enough to be accounted for by manufacturing variance between individual samples.
    That's good enough for me.
    Ken

    http://www.jkwynn.co.uk/
    DIY Technics/ProJect based Turntable + Terminator linear tracker + AT 33PTG II / AQVOX Phono 2 CI / Pro-Ject Pre Box RS / ESP Active X-Over / Nord MC500 Power Amps/ Modified semi-active Yamaha NS1000M Speakers / Stello CDT100 Transport / NAD M51 DAC.

  5. #55
    Join Date: Jun 2008

    Location: N. Ireland

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    I'm Steve.

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    Quote Originally Posted by Qwin View Post
    DATS has a lot of functions other than T&S perimeters, Signal Generator, Oscilloscope, so calibration is worth while.

    Agreed T&S Parameters and box calculators give ball park results which need fine tuning.

    You still missed my point on the measuring, Its the difference between the two measurements on its back, or the difference between the two mounted vertical. I realize they will be different sets of measurements.
    The driver will have a pair of measurements on its back and a pair mounted vertical.
    But will the DIFFERENCE between the bare/Loaded measurements be the same for both attitudes?
    I don't know how you would load a vertical driver anyway, you would have to use one of the other methods.

    This software is used by many people and also Dayton Audio, who designed the software for in house use, before selling it to the public. I've seen the DATS logo in the corner of other manufacturer info as well, so it must work.
    Maybe the software takes account of the driver orientation, who knows.
    Seems pretty pointless trying to think of reasons it might not work, when you don't know what the designers have taken into account in the software.
    Measure a driver with known properties and the measurements are damn close to them, close enough to be accounted for by manufacturing variance between individual samples.
    That's good enough for me.
    I no d of alluded to this in an earlier post, ie that the software may have been written to take into account gravity when measuring a driver on its back. I can also only calculate the cone volume to a certain degree of accuracy since this is a DC driver with a gaping hole in the middle ( the tulip guide for the HF driver) I might make 2 sets of measurements, one using added mass and the other with the sealed box method. I think given the potential error on the sealed box volume the added mass may even be more reliable? But I imagine in the great scheme of things it will all work out in the end. Of course all this time, expense and stress could have been avoided had Tannoy released the numbers to me! Well love his a road we travel, and there are bumps along the way, I am just glad other more experienced people are here to offer help and advice!

    Steve

    Sent from my SM-G960F using Tapatalk
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  6. #56
    Join Date: Nov 2011

    Location: wirral

    Posts: 188
    I'm frank.

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    With nothing to do this afternoon I did a youtube trawl of manufacturers testing rigs ; Seas vertical, Eminence face down, Tannoy face down, Dynaudio 30', ATC on its back and face-down.
    As mentioned earlier get the driver free of any tabletop reflections-placed on a pedestal is prob best. Remember its meant to be fun..

  7. #57
    Join Date: Jun 2008

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    I'm Steve.

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    Quote Originally Posted by cooky View Post
    With nothing to do this afternoon I did a youtube trawl of manufacturers testing ; Seas vertical, Eminence face down, Tannoy face down, Dynaudio 30', ATC on its back and face-down.
    As mentioned earlier get the driver free of any tabletop reflections-placed on a pedestal is prob best. Remember its meant to be fun..
    Cheers Cooky. There are more variables and possibilities than I though possible. When you say Tannoy face down, I assume you mean into a sealed box? Also, when you mention the pedestal, you mean using the added mass method?

    Steve

    Sent from my SM-G960F using Tapatalk
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  8. #58
    Join Date: Nov 2011

    Location: wirral

    Posts: 188
    I'm frank.

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    Yes I'm sure there's no right or wrong way just 'both 'ways to be sure!
    What I mean by face down is the driver firing down into a box-thats installed under a workbench.
    By pedestal I just mean sit the driver away from any flat surface that can reflect back to the cone, i put my test drivers on a 30cm tall stack of books(!)when doing free air T&S, I've found with VAS the known volume method easier and more consistent to do than added mass-remember you must remove any cab damping.

  9. #59
    Join Date: Jun 2008

    Location: N. Ireland

    Posts: 2,486
    I'm Steve.

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    Quote Originally Posted by cooky View Post
    Yes I'm sure theres no right or wrong way just 'both 'ways to be sure!
    What I mean by face down is the driver firing down into a box-thats installed under a workbench.
    By pedestal I just mean sit the driver away from any flat surface that can reflect back to the cone, i put my test drivers on a 30cm tall stack of books(!).
    Great, I assume then that you use the added mass method. The suspension on these drivers is very 'stiff' much more son that the on the 6.5" mid bass on my usual speakers. I missed out on a set of minidsp plate amps that would have meant I could have gone active with just the Tannoy, or stayed passive and added an additional bass driver if required. We shall see.

    Steve

    Sent from my SM-G960F using Tapatalk
    They swim... the mark of Satan is upon them. They must hang.


    FLAC / WDTV Live / Cambridge Audio / Tannoy VX12

  10. #60
    Join Date: Nov 2011

    Location: wirral

    Posts: 188
    I'm frank.

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    Quote Originally Posted by aquapiranha View Post
    Great, I assume then that you use the added mass method. The suspension on these drivers is very 'stiff' much more son that the on the 6.5" mid bass on my usual speakers. I missed out on a set of minidsp plate amps that would have meant I could have gone active with just the Tannoy, or stayed passive and added an additional bass driver if required. We shall see.

    Steve

    Sent from my SM-G960F using Tapatalk
    No, face down into an enclosure for VAS and on its back for free air T&S and a quick test in vertical just to be sure.

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